The present invention relates to an optical access network in an optical communication system; and more particular, to an optical line termination (OLT) in an asynchronous transfer modexe2x80x94passive optical network (ATMxe2x80x94PON).
A conventional optical access network uses a pair of optical cables per subscriber. One of the pair of optical cables is used for time division multiplexing (hereinafter, referred to as TDM) in a downstream direction, and the other of the pair of optical cables is used for time division multiple access (hereinafter, referred to as TDMA) in an upstream direction, thereby transmitting a voice, integrated services digital network (ISDN) and digital television signals. Therefore, an initial installation cost of the optical cable is very high and it is difficult to provide various and flexible services.
It is, therefore, an object of the present invention to provide an optical line termination (OLT) in an asynchronous transfer modexe2x80x94passive optical network (ATMxe2x80x94PON), capable of providing a maximum ATM servicing capacity and reducing a manufacturing cost.
In accordance with an aspect of the present invention, there is provided an optical line termination in an asynchronous transmission mode, comprising: a downstream frame processing means for receiving and churning an asynchronous transfer mode cell to generate a downstream frame, and converting a parallel data of the downstream frame into a serial data thereof; a wavelength division multiplexing means for performing an electro/optical conversion of the serial data of the downstream frame and performing a wavelength division multiplexing thereof; an upstream frame processing means for extracting data from the wavelength division multiplexing means, searching an overhead field, delineating a slot boundary, and processing a PLOAM cell and a divided slot separately; a control signal generation means for performing a MAC protocol and generating variables and timing signals used for the downstream frame processing means and the upstream frame processing means; and a control means for controlling the downstream frame processing means and the upstream frame processing means by using the variables and the timing signals from the control signal generation means.
In accordance with another aspect of the present invention, there is provided a churning method in an asynchronous transfer mode, comprising the steps of: a) requesting a new churning key through a new key request message to an ONU, wherein the ONU completes a distance measurement; b) transmitting the new churning key to the OLT through the new key request message; c) in case where the OLT receives the new churning key predetermined times, transmitting a churning key update message to the ONU predetermined times at a predetermined interval together with a transmission numbers; and d) after receiving a first correct churning key update message, transmitting an acknowledge signal representing a message reception to the OLT.
In accordance with further another aspect of the present invention, there is provided a method for allocating a down message in an optical line termination, comprising the steps: a) in case where a current state is not an express message slot and a message memory is empty, transmitting a serial number mask message and a request password message one time; b) transmitting the other message three times, thereby determining the transmission numbers according to a message identification read out from a memory; and c) in case where the message memory is empty and is not the express message slot, transmitting a NO message.